I offered two rak'ahs of prayer before the Maghrib prayer (i.e. obligatory) during the time of the Messenger of Allah (ﷺ). I (narrator al-Mukhtar b. Fulful) asked Anas: Did the Messenger of Allah (ﷺ) se you ? He replied: Yes, but he neither commanded us nor forbade us (to do so).
Sunan Abi Dawud Book 5, Hadith 33
← Previous Hadith The Messenger of Allah (ﷺ) said: Pray two rak'ahs before the Maghrib prayer. He then said (again): Pray two rak'ahs before the Maghrib prayer, it applies to those who wish to do so. That was because he feared that the people might treat it as sunnah.

Sunan Abi Dawud Book 5, Hadith 32 Next Hadith → The Messenger of Allah (ﷺ) as saying: Between the two adhans there is a prayer, between the two adhans there is prayer for one who desires (to offer).

Sunan Abi Dawud Book 5, Hadith 34